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# A juggler maintains four balls in motion making each of them raise to a height of 20m from his hand.What time interval should he maintain, for the proper distance between them $(g=10 m/s^2)$

$(a)\;3s\quad (b)\;\frac{3}{2}s \quad (c)\;2s \quad (d)1 s$

For each ball
$v^2-u^2=2as$
$\quad -u^2=2(-10)20$
$\qquad u=20 m/s$
also $v=u+at$
$\qquad 0=20-10 t$
$\qquad t=2 sec$
so total time is 4 seconds
so each ball must be thrown at interval of $\large\frac{4}{4}$$=1 sec$ to maintain proper distance
Hence d is the correct answer.

edited Jan 25, 2014 by meena.p

+1 vote